Large industrial facilities, such as nuclear power stations, petroleum refineries, and chemical process plants, use large numbers of motor-operated valves, or similar switching devices, such as solenoid valves or air-operated valves, for process control. All of these switching devices require periodic maintenance to assure their continued operability and to enable the economic and safe operation of the facility. Unfortunately, maintenance expenses at such facilities are high, due in large part to both direct costs and the costs of lost production when equipment must be removed from service to perform the maintenance. Because of these high maintenance expenses, there is a great need in the art for low cost testing and evaluation techniques to accurately assess the current operating condition of such switching devices, and to further reliably predict when such devices need to receive maintenance.
A number of test techniques exist in the art for testing a motor-operated valve, each having its own advantages and disadvantages These techniques include: manually measuring the time required for the valve to move from one state to another (referred to as "valve stroke timing"), monitoring motor current and power, and determining the valve operator thrust (the amount of force or torque delivered by the motor or other device used to operate the valve) during valve stroking. Probably the most reliable and repeatable test technique available for evaluating the operability of a motor-operated valve is to determine the valve operator thrust, as data obtained from such a test will not change significantly unless some problem has developed or is beginning to develop. Data analysis techniques, known in the art, may then be used to monitor the data obtained from such operator thrust tests to predict when such a valve needs maintenance and to prevent a breakdown condition from developing. Unfortunately, this is the most expensive and difficult test to perform because it requires physical access to the equipment, in this case a valve, and intrusion into or removal of the equipment to couple the measuring equipment, thereby requiring that the facility wherein the equipment is located be shut down. Hence, this technique is not preferred unless the facility is shut down for other reasons.
The current preferred motor-operated valve test requirement for nuclear power plants, valve stroke timing, is set forth in the 1986 edition of the American Society of Mechanical Engineers' Boiler and Pressure Vessel Code (ASME Code), Section XI, Subsection IWV. This timing test is carried out manually, using a stopwatch in the central control room, while observing valve position indicator lights. This test offers the advantage of being simple to perform, does not require attendance at the site of the equipment, and does not require any intrusion into the equipment. Unfortunately, this is the least reliable test to perform, not only because of the human element involved in manually operating a stopwatch but also because the evaluations specified by the ASME Code are not specific to individual motor-operator capabilities, which capabilities vary significantly. The human element can seriously affect the accuracy and repeatability of the data, thereby rendering the data obtained of little use for data and statistical analysis purposes. What is needed in the art is an improved motor-operated valve testing technique that offers the reliability and repeatability features of the valve operator thrust tests, while at the same time offers the non-invasive and simplicity advantages of the stroke timing test. The present invention is advantageously directed to such a testing technique.